Surface modification of recycled coarse aggregate based on Microbial Induced Carbonate Precipitation

Recycled aggregates (RAs) are wrapped by hardened mortar, which has high porosity and low strength, therefore hinders the direct application of RAs in concrete industry. In order to improve the performance of recycled aggregate concrete, bio-deposition has been developed for the surface modification of RAs, the process involves the formation and the accumulatation of sediments on the aggregate surface. In this work, the effects of Microbial Induced Carbonate Precipitation (MICP) on the properties of RAs based on urea decomposition precipitation system (system N) and CO2 capture precipitation system (system C) were investigated. It was demonstrated that the direct immersion treatment of the RAs under system N had the best modification performance. The mass increase of the RAs after 28 days reached 12% and the water absorption rate was reduced by 33%. Moreover, due to the strong adhesion between the sediments and the Ras' surface, the elastic modulus and hardness of the interfacial transition zone increased by 16.9% and 40.7%, respectively. Although the overall modifcation performance of system N was superior than that of system C, the latter method presented an environmentally friendly approach since CO2 was captured and immoblized. By revealing the MICP mechanisms on RAs’ surface, this work inspires the design of other distinctive bio-modification strategies for RAs in concrete applications.